Field of the Invention
This invention relates to the field of removing non-metallic coatings from metal objects, and more particularly, it concerns removing layers of paint from coated metal hangers.
In many manufacturing operations, a newly made part or product is spray painted either with paint particles in a solvent, or with electrostatic powder coatings, and this occurs in many fields including automobile, appliance, metal furniture, tractors, and so on. In many cases, the parts are sprayed while being conveyed along a production line while the parts are suspended from metal hangers spaced along a conveyor system that carries the parts through a spraying station. As time goes on, these metallic hangers become covered with layer upon layer of paint and in time they become unusable. For example, they may become so coated that they won't conduct electricity to maintain an electrostatic charge.
Accordingly, it becomes a problem to remove the accumulated layers of paint from the metal hangers and restore the hangers to service. One solution has been proposed that uses solvents to dissolve the paint layers from the metal hanger. Another solution proposes burning off the non-metallic coatings. Another proposes impacting the coated hanger after embrittling the non-metallic coating by subjecting the coated hanger to extremely low temperatures, and also debonding the coating from the metal hanger by causing the coatings and the metal to contract at different rates to draw the faster-contracting metal away from the slower-contracting coatings.
U.S. Pat. No. 3,934,379 discloses a method for removing layers of organic material built up on a support for articles during surface finishing which includes the steps of rapidly reducing the temperature of a coated metal support, or of the coatings, to lessen the bonded relation between the coating layers and the support, to embrittle the coating, and to remove the coating by impacting the coating while it is still in a refrigerated state.
U.S. Pat. No. 4,205,530 discloses an apparatus and method for removing hard rubber tires from metal wheels by freezing and shrinking the rim of the wheel without freezing or shrinking the rubber tire to thereby pull the metal rim away from the tire so that the hard rubber tire can be removed easily without subjecting it to impact stress.